The immunoglobulin superfamily (IgSF) consists of numerous genes that code for proteins with diverse functions, one of which is intercellular adhesion. IgSF proteins contain at least one Ig-related domain that is important for maintaining proper intermolecular binding interactions. Because such interactions are necessary to the diverse biological functions of the IgSF members, disruption or aberrant expression of many IgSF adhesion molecules has been correlated with many human diseases.
The carcinoembryonic antigen (CEA) belongs to a subfamily of the Ig superfamily consisting of cell surface glycoproteins known as CEA-related cell adhesion molecules (CEACAMs). CEACAMs have been shown to act as both homotypic and heterotypic intercellular adhesion molecules (Benchimol et al., Cell 57: 327-334 (1989)). In addition to cell adhesion, CEA (also known as CEACAM5) inhibits cell death resulting from detachment of cells from the extracellular matrix and can contribute to cellular transformation associated with certain proto-oncogenes such as Bcl2 and C-Myc (see Berinstein, J. Clin Oncol. 20(8): 2197-2207 (2002)). Sequences coding for human CEA have been cloned and characterized (U.S. Pat. Nos. 5,274,087; 5,571,710; and 5,843,761. See also Beauchemin et al., Mol. Cell. Biol. 7:3221-3230 (1987); Zimmerman et al., Proc. Natl. Acad. Sci. USA 84:920-924 (1987); Thompson et al. Proc. Natl. Acad; Sci. USA 84(9):2965-69 (1987)).
Normal expression of CEA has been detected during fetal development and in adult colonic mucosa. CEA overexpression was first detected in human colon tumors over thirty years ago (Gold and Freedman, J. Exp. Med. 121:439-462 (1965)) and has since been found in nearly all colorectal tumors. Additionally, CEA overexpression is detectable in a high percentage of adenocarcinomas of the pancreas, liver, breast, ovary, cervix, and lung. Because of its prevalence in these tumor types and limited normal tissue expression, CEA is considered a self tumor-associated antigen and a target for active and passive immunotherapy. Recent clinical data have established that different vaccine strategies can generate human B and T cells specific for CEA, providing additional evidence that CEA is a target for molecular and immunological intervention for treatment of these cancer types.
Therapeutic approaches targeting CEA include the use of anti-CEA antibodies (see Chester et al., Cancer Chemother. Pharmacol. 46 (Suppl): S8-S12 (2000)), as well as CEA-based vaccines (for review, see Berinstein, supra). The development and commercialization of many vaccines have been hindered by difficulties associated with obtaining high expression levels of exogenous genes. Success of DNA-based vaccines has also been hindered by an inability to generate an immune response of sufficient magnitude in treated individuals. Although DNA vaccines targeting various proteins have been developed, the resulting immune responses have been relatively weak compared with conventional vaccines.
The ease of DNA manipulation has offered an opportunity to develop vaccines incorporating gene fusion strategies in which antigens are linked to various immunoenhancing elements. Enhancement of immune response to target antigens has been demonstrated in animal models by vectors encoding antigens fused to heat shock protein (HSP) 70 (Liu et al., J. Virol. 74: 2888-94 (2000); Cheng et al. J. Immunol. 166: 6218-26 (2001); Chen et al., Cancer Res. 60: 1035-42 (2000)), to Fc portion of IgG1 (You et al., J. Immunol. 165: 4581-92 (2000)), to lysosome-associated membrane protein (LAMP) (Su et al., Cancer Res. 62: 5041-48 (2002)), and universal Th epitope from tetanus toxin (Renard et al., J. Immunol. 171:1588-95 (2003); King et al., Nature Med. 4: 1281-86 (1998); Lund et al., Cancer Gene Ther. 10: 365-76 (2003); Padua et al., Nature Med. 9(11): 1413-17 (2003); Savelyeva et al., Nature Biotechnol. 19: 760-64 (2001); Wahren et al., WO 2004/092216). The enhancement of immune responses to target antigens is particularly relevant for cancer vaccines in view of the limited immunogenicity of tumor antigens and of the need to overcome tolerance to exert effective antitumor effects.
Therefore, despite the identification of the wild-type nucleotide sequences encoding CEA proteins described above, it would be highly desirable to develop a vaccine which is capable of eliciting an enhanced CEA-specific immune response relative to a wild-type full-length CEA cDNA, when delivered to a mammal. It would also be desirable to develop methods for treating or preventing CEA-associated cancers which utilize nucleic acid molecules or proteins that safely and effectively potentiate a CEA-specific immune response.